Integrated circuit package with flat topped heat sink

Abstract: An integrated circuit package is disclosed, of the type having a pin-fin heat sink attached to the surface. A flat plate is attached to the ends of the pins of the heat sink, to provide a planar surface area of adequate size to allow a vacuum pickup tool to pick and place the packaged integrated circuit, and to receive marking and symbolization.

Description: This invention is in the field of integrated circuits, and more specifically is in the field of integrated circuit packaging. IBM Technical Disclosure Bulletin Vol. 27 No. 3 August 1984, New York, US p. 1438, S. Furkay et al, "Integral Heat Sink/Module Cap" discloses an IC package having a flat surface, and a heat sink attached thereto. The heat sink has a plurality of extension extended away from the IC package. A plate is attached to the ends of the extensions, the plate having a flat surface that is substantially parallel with the flat surface of the IC package. A plate is attached to the ends of all the extensions of the heat sink. IBM Technical Disclosure Bulletin Vol. 36 No. 12 December 1983, New York, US p. 625 to 626 "Heat Sink Stand for Fully Encapsulated Substrate" there is disclosed the use of a thermally conductive adhesive for connecting a heat sink stand to a surface with a chip. Many modern integrated circuits, especially those of the microprocessor type, now integrate upwards of hundreds of thousands of transistors into a single semiconductor chip to provide a high degree of functionality at very high speeds. Even when utilizing low-power technologies such as complementary metal-oxide-semiconductor (CMOS) technology, these ultra-large-scale integrated (ULSI) circuits dissipate significant electrical power, for example more than one watt. As is well known in the art, the electrical power dissipated in an integrated circuit is often manifest as thermal energy in the semiconductor chip. This thermal energy will tend to elevate the temperature of the semiconductor chip. As is well known in the art, both the switching speed and the reliability of an integrated circuit decrease with increasing temperature. As a result, integrated circuit package design is highly concerned with the conduction of thermal energy away from the semiconductor chip, such conduction taking place through the package, in an attempt to minimize performance and reliability degradation due to high operating chip temperatures. Referring now to Figure 1, a conventional integrated circuit package for providing high thermal conductivity is illustrated. In this example, the semiconductor chip is housed within pin-grid-array package 2. As is conventional in the art, pin-grid-array package 2 is a ceramic header, within which the semiconductor chip is mounted and its conductive terminal pads bonded, by wire bonds or the like, to pins extending from the bottom of pin-grid-array package 2; a ceramic or metal lid is then bonded to the header by way of glass reflow, brazing, or by way of other conventional techniques. In the example shown in Figure 1, heat sink 4, of the "pin-fin" type, is mounted to the top surface of pin-grid-array package 2. Heat sink 4 is conventionally formed of extruded aluminum or another thermally conductive material, and includes a flat lower portion 4f that is attached to pin-grid-array package 2 by way of a thermally conductive epoxy, or by other conventional means. The upper portion of heat sink 4, as shown in Figure 1, includes a large number of finger-like extensions, or pins, 4e extending away from pin-grid-array package 2. Extensions 4e are responsible for nearly all of the surface area of heat sink 4. As such, extensions 4e will provide a highly thermally conductive path from pin-grid-array package 2 to the atmosphere thereabove, without greatly increasing the overall height of the package combination. Especially if a flow of cool air passes over and through extensions 4e, conventional heat sink 4 can be quite useful in removing thermal energy from the semiconductor chip packaged in pin-grid-array package 2. However, considering that heat sink 4 is generally attached to pin-grid-array package 2 by the manufacturer of the integrated circuit, the arrangement of Figure 1 suffers from certain limitations. Firstly, many computer and system manufacturers use vacuum pickup tools to transport and install packaged integrated circuits into circuit boards; this is especially the case for system manufacturers that use automated pick-and-place robotic machines in circuit board assembly. However, vacuum pickups cannot readily be used with the arrangement of Figure 1, as there is not adequate planar surface area on its top to allow a vacuum pickup to reliably attach to heat sink 4 (and thus to lift and transport pin-grid-array package 2). This may require manual installation of the package of Figure 1, at greater cost and often reduced accuracy. Secondly, there is also not enough coplanar surface area on the upper surface of the integrated circuit package of Figure 1 to allow the manufacturer or purchaser of the integrated circuit to mark the packaged circuit with a code, part number, or manufacturer identification. Particularly if multiple integrated circuits similarly packaged are to be mounted to the same circuit board, the arrangement of Figure 1 can result in manufacturing defects in the end system with the wrong integrated circuit mounted at the wrong circuit board location. It is therefore an object of the present invention to provide an integrated circuit package utilizing pin-fin thermal conduction and that may be mounted by vacuum pickup equipment. It is a further object of the present invention to provide such an integrated circuit package that allows for topside symbolization and marking after manufacture. Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art having reference to the following specification together with its drawings. According to one aspect of the present invention there is provided an integrated circuit device, comprising an integrated circuit package, containing an integrated circuit chip, and having a flat surface, a heat sink attached to the flat surface of the integrated circuit package, said heat sink having a plurality of extensions extending away from the integrated circuit package and a plate attached to the ends of the extensions and having a flat surface that is substantially parallel with the flat surface of the integrated circuit package, characterised in that the plate is smaller than the plan area of the heat sink and the package and is not attached to at least one of the plurality of extensions. According to another aspect of the present invention there is provided a method of manufacturing an integrated circuit device, comprising mounting an integrated circuit chip within an integrated circuit package, the integrated circuit package having a flat surface, attaching a heat sink to the flat surface of the integrated circuit package, the heat sink having a plurality of extensions extending away from the integrated circuit package after the attaching step and attaching a plate to the ends of the extensions of the heat skink, characterised in that the plate is smaller than the plan area of the heat sink and the package and the step of attaching the plate comprises attaching the plate to some, but not all, of the plurality of extensions. The invention may be implemented into an integrated circuit package which has a pin-fin heat sink attached to its exposed surface. A flat plate, preferably of a thermally conductive material, is attached to the tops of the heat sink pins so that the pins are substantially orthogonal to the plate. The flat plate provides a coplanar surface by way of which a vacuum pickup may pick and place the integrated circuit package, and upon which conventional device marking may be placed. The exposed surface of the plate may be flush with, or extend above, the ends of the heat sink pins. Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a conventional integrated circuit package, of the pin-grid-array type, with a heat sink of the pin-fin type attached thereto. Figure 2 is an exploded perspective view of an integrated circuit package according to a first preferred embodiment of the invention. Figure 3a is a cross-sectional elevation view of the integrated circuit package of Figure 2, after assembly. Figure 3b is a cross-sectional elevation view of an integrated circuit package according to an alternative embodiment of the invention. Referring now to Figure 2, a first preferred embodiment of the invention will now be described in detail. As shown in the exploded perspective view of Figure 2, this embodiment of the invention includes pin-grid-array package 2, similarly as in the conventional package arrangement discussed above relative to Figure 1. Of course, package 2 may be implemented as a ball-grid-array package, a chip carrier, a dual-in-line package, or an integrated circuit package of other conventional type having a flat surface that will be exposed when package 2 is mounted to a circuit board. Also similarly as discussed above relative to the conventional arrangement of Figure 1, pin-fin heat sink 4 is also provided, having a flat portion 4f for mounting to the surface of package 2 in a thermally conductive fashion, such as by way of a thermally conductive epoxy, solder, or the like. Figure 3a illustrates the package arrangement of Figure 2 after its assembly, including epoxy layer 3 disposed between the surface of package 2 and the bottom of flat portion 4f of heat sink 4. Also as discussed above, heat sink 4 also includes extensions 4e, which extend away from package 2 and which provide a large surface area for heat sink 4, thus improving the thermal conduction between it and the atmosphere surrounding the package. According to the present invention, plate 6 is provided for mounting to the ends of extensions 4e of pin-fin heat sink 4. Figure 3a illustrates, in cross-section, plate 6 after mounting to the ends of extensions 4e, such mounting preferably made by way of a conductive epoxy 5. Plate 6 is preferably formed of aluminum, or of another thermally conductive material, to provide additional thermal conduction to the atmosphere; alternatively, if the thermal conduction provided by heat sink 4 is otherwise adequate, plate 6 may be formed of plastic or another conventional material, with the adhesive between it and extensions 4e selected accordingly. Plate 6 is somewhat smaller than the plan area of heat sink 4 and package 2, as the dimensions of plate 6 need only be as large as necessary to provide easy vacuum pickup by conventional vacuum pick-and-place equipment, and to accomplish the desired marking or symbolization (such marking illustrated in Figure 2). This is preferred, as full coverage of the plan area of heat sink 4 with plate 6 may impede the flow of coolant air thereover. For example, plate 6 may be on the order of 20 mm square. Further in the alternative, plate 6 may be formed integrally with heat sink 4, so that no additional attachment step is required. A separately attachable plate 6 is preferred, however, as this allows for heat sink 4 to be extruded, as an integrated heat sink and plate would likely require a more complicated manufacturing process. As will be evident from Figure 2, plate 6 provides adequate planar surface area to allow the combination of package 2, heat sink 4, and plate 6 to be lifted, transported, and placed by conventional vacuum pickup tools, whether operated by hand or by robot. Further, plate 6 provides an exposed planar surface area adequate to receive marking with the manufacturer's identifying name or mark, with a part number, with a performance grade indicator, or the like. Figure 2 illustrates plate 6 as marked with a manufacturer's trademark, for example. As a result, the package according to the present invention overcomes the limitations of conventional pin-fin heat sink integrated circuit packages, such as that shown in Figure 1, which are necessarily incompatible with vacuum pickup equipment and which are not readily marked with manufacturer identifiers, part numbers, and the like. Referring now to Figure 3b, an alternative embodiment of the invention will now be described. According to this alternative embodiment of the invention, extensions 4e' are shorter in the interior of heat sink 4' than at the perimeter, so that the exposed top surface of plate 6' will be flush with those of extensions 4e' to which plate 6' is not mounted. This alternative embodiment of Figure 3b may be preferred over that of Figure 3a, in those cases where the manufacturing processes involve lateral forces across the top of heat sink 4; in the embodiment of Figure 3b, plate 6' will be less prone to inadvertent removal from heat sink 4' by such a lateral force. While the invention has been described herein relative to its preferred embodiments, it is of course contemplated that modifications of, and alternatives to, these embodiments, such modifications and alternatives obtaining the advantages and benefits of this invention, will be apparent to those of ordinary skill in the art having reference to this specification and its drawings. It is contemplated that such modifications and alternatives are within the scope of this invention as subsequently claimed herein.

Claims: An integrated circuit device, comprising: an integrated circuit package (2), containing an integrated circuit chip, and having a flat surface; a heat sink (4f) attached to the flat surface of the integrated circuit package (2), said heat sink (4f) having a plurality of extensions (4e,4e') extending away from the integrated circuit package (2); and a plate (6,6'), attached to the ends of the extensions (4e,4e'), and having a flat surface that is substantially parallel with the flat surface of the integrated circuit package (2), characterised in that the plate (6,6') is smaller than the plan area of the heat sink (4f) and the package (2) and is not attached to at least one of the plurality of extensions (4e,4e'). The integrated circuit of claim 1, further comprising: means (5) for attaching the plate (6,6') to the ends of the extensions (4e,4e'). The integrated circuit of claim 2, wherein the attaching means (5) comprises a thermally conductive epoxy. The integrated circuit of claim 1, wherein the plate (6,6') is formed integrally with the heat sink (4f). The integrated circuit of claim 1, wherein the integrated circuit package (2) is of the pin-grid-array type. The integrated circuit of claim 1, wherein the integrated circuit package (2) is of the ball-grid-array type. The integrated circuit of claim 1, further comprising: marking on the flat surface of said plate (6,6'). A method of manufacturing an integrated circuit device, comprising: mounting an integrated circuit chip within an integrated circuit package (2), the integrated circuit package (2) having a flat surface; attaching a heat sink (4f) to the flat surface of the integrated circuit package (2), the heat sink (4f) having a plurality of extensions (4e,4e') extending away from the integrated circuit package (2) after the attaching step; and attaching a plate (6,6') to the ends of the extensions (4e,4e') of the heat sink (2f), characterised in that the plate (6,6') is smaller than the plan area of the heat sink (4f) and the package (2) and the step of attaching the plate comprises attaching the plate to some, but not all, of the plurality of extensions. The method of claim 8, wherein the step of attaching the plate (6,6') comprises epoxying the plate to the ends of the extensions (4e,4e') of the heat sink with a thermally conductive epoxy (5). The method of claim 8, wherein the step of attaching the plate (6,6') comprises integrally forming the plate (6,6') with the heat sink (4f). The method of claim 8, further comprising: marking an exposed surface of the plate (6,6') after the step of attaching the plate (6,6').

Inventors: HUNDT MICHAEL J, HUNDT, MICHAEL J.
Applicants: ST MICROELECTRONICS INC, STMICROELECTRONICS, INC.
Application year: 1994
Main classification: H01L23
IPC codes: H01L23